The kinetic energy of moving wind has been converted by various devices into mechanical motion to accomplish useful work for many centuries. This energy has been used to pump water, grind grains, provide mechanical power for a variety of uses, and in this century, generate electricity. The overwhelming majority of these devices rely on an air foil or sail to convert the linear motion of the wind to rotational motion of a windmill shaft.
Rotary windmills are divided into two main categories depending on whether the axis of rotation is oriented in a horizontal or vertical plane. The oldest known horizontal axis windmills were the post mills, the predecessors of the "Dutch" windmills. The American multi-vane fan type windmills gained considerable use in the American west during the late 19th century as water pumpers. More recently, the propeller-type windmills have become popular because of their higher efficiency and small blade area.
A horizontal axis windmill requires a tower strong enough to withstand the axial forces produced by the blades, a device to orient the blades to face the wind, a feathering device to give protection from strong winds, and a series of gears to convert the rotational speed of a shaft to the optimal speed for the desired use. In most designs, the windmill must be located at the top of a tower, complicating its installation, maintenance and repair.
There are a variety of vertical axis machines now being used or under development. They include wind turbines, Savonius rotors, Darrieus rotors, giromills, vortex generators and several other concepts. Vertical axis machines generally do not need to be oriented toward the wind, and some types do not require towers. These advantages are offset, however, by a significantly lower efficiency of extracting power from the wind. In addition, the most popular type, the Darrieus rotor, is not self-starting, and structural stability problems may significantly limit the useful lifetime. Almost all of the vertical axis machines used for power production require gear reduction systems and large structures that rotate at high velocities.
Traditionally, windmills have been used extensively for pumping water, producing small amounts of electricity at remote sites, and more recently in large scale multi-megawatt installations. In the past few years, a variety of horizontal axis, kilowatt sized windmills have become available for home or farm use. However, there are a number of objections to using windmills in residential or urban settings. The tower and equipment involved often clash aesthetically with the residential environment. The tower height and high rotational velocity of the blade tips can pose significant safety problems. Also there are problems with television interference caused by varying reflections from the blades.
Further, the costs for these machines are high because the number of units manufactured is not large enough to take advantage of mass production techniques.
In a more general sense, the kinetic energy of a moving fluid may be converted to the motion of a solid body in a variety of ways. Sail boats, ice boats, and vehicles equipped to run on rails have been used to convert wind power to linear motion. In a prior device that is disclosed in U.S. Pat. No. 3,987,987, issued on Oct. 26, 1976 to Peter R. Payne, a self-erecting windmill uses the back and forth motion of tethered air foils to extract wind energy by forcing the tethering line to turn a shaft.
In U.S. Pat. No. 4,024,409, issued on May 17, 1977 to Peter R. Payne, a device is disclosed that uses cylindrical cables to extract wind energy by inducing a transverse oscillatory motion. Mechanical power is extracted from the system by use of a diaphragm pump. In the same patent, a device is proposed to generate electricity by the motion of the cable in a magnetic field produced by permanent magnets. All of the devices discussed in this patent rely on the induced lateral motion of a cylindrical cable in the wind. It is a well known result that the power flow through the cross section of a cable is proportional to the square of the lateral displacement, the tension of the cable to the three halves powers, and is inversely proportional to the length of the cable. To obtain significant power from a vibrating cable, both the lateral motion and the tension in the cable must be high. However, the wind will not induce large amplitude motion in a tight cable unless it is long. Further, since the power in the cable is inversely proportional to its length, devices based on the lateral motion of cylindrical cables cannot efficiently extract energy from the wind or deliver power commensurate to their size.
Another significant drawback of these devices is that they suffer from a lack of an energy conversion system or transducer portion of the device that is well matched to the characteristics of the wind energy collector portion of the device. In addition, the motion of the cable will not generally be confined to a plane, causing the cables to hit the magnets. Further, the device is proposed for use in single units, not a coordinated set of devices to scale to the desired power. Another disadvantage of the device is that it uses heavy and expensive permanent magnets to provide the magnetic field. Another complication arises because the cylindrical cable must always oscillate with a motion perpendicular to the magnetic field such that a guiding vane is necessary to orient the magnets in the proper direction. The limitations engendered in vibrating systems that rely on lateral motion of cylindrical cables leave open the possibility of other shapes and types of motions that can more efficiently couple wind energy to a vibrating member.
The present invention is directed to overcoming one or more of the problems as set forth above.